High speed microwave phase shifter using a positionable electron beam to cause electromagentic-wave reflection



ABLE MAGNETIC-WAVE 2 Sheets Feb, 28, 1967 SHELEG ET AL HIGH SPEED MICROWAVE PHASE SHIFTER USING A POSITION ELECTRON BEAM TO CAUSE ELECTRO REFLECTION --Sheet 1 Filed May 21 1963 INVENTOR5 BOR I S S H ELEG B l LLY D. W R I G HT ATTORNEY Feb. 28, 1967 SHELEG ET AL 3,397,194

HIGH SPEED MICROWAVE PHASE SHIFTER USING A POSITIONABLE ELECTRON BEAM TO CAUSE ELECTED-MAGNETIG-WAVE REFLECTION File M y El, 1963 2 Sheets-Sheet 2 I 1,; Eli 32 34 |o 3s ELECTRON DIRECTIONAL 36 BEAM COUPLER PHASE TERM'NAT'ON SHIFTER RF. OUTPUT I 1AE;5

|0 lo BEAM BEAM PHASE PHASE SHI FTEF? SHI FTER TEE JUNCTION INVENTORS BORIS SHELEG BILLY D.WFHGHT ATTORNEY United States Patent HIGH SPEED MICROWAVE PHASE SHIFTER USING A POSITIONABLE ELECTRON BEAM T0 CAUSE ELECTROMAGENTIC-WAVE RE- ELECTION Boris Sheleg, Fort Washington Estates, Md. (3801 Calvert Lane, Washington, D.C. 20022), and Billy D. Wright, 0x011 Hill, Md. (5620 Fargo Ave., Washington, D.C. 20021) Filed May 21, 1963, Ser. No. 282,183 Claims. (Cl. 343701) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a high speed phase shifter and more particularly to a microwave phase shifter employing an electron beam.

In general the means of rapidly phase shifting microwave energy in scanning arrays and microwave systems heretofore available have been in the nature of line stretchers, frequency changers, and ferrite phase shifters. The line stretchers and ferrite phase shifters have a relatively slow response time, While the frequency changer, which has a fast enough response time, has limitations when used in scanning arrays.

The present invention is an electronic phase shifter employing an electron gun emitting a stream of electrons across a waveguide requiring neither frequency change nor additional material to eflfect a phase shift.

An object of the present invention is the provision of a high-speed phase shifter.

Another object is to provide an electronic on-off switch.

A further object of the invention is the provision of a power monitor.

Still another object is to provide an amplitude modulator.

A final object of the present invention is theprovision of a variable attenuator.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate preferred embodiment, and wherein:

FIG. 1 shows an isometric view of the present invention.

FIG. 2 illustrates how the present invention is integrated into a complete system to provide a variablephase to an antenna.

FIG. 3 is a block diagram showing how two units of the instant invention may be incorporated and combined in a system to provide a scanning antenna.

Briefly, the invention embodies a waveguide which has a longitudinal slot therein, with anelectron gun providing an electron beam into the longitudinal slot and across the waveguide. By deflecting the beam along the longitudinal slot, the phase angle of the energy projected into the waveguide can -be effectively phased, modulated, attenuatedd, or completely blocked.

Referring now to the drawings in detail, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 an electronic phase shifter in the form of a tube 10 which may 'be made of metal, glass, or the like, mounted on a waveguide 12, with the waveguide having a longitudinal slot 14 and windows 15 at each end. Tube 10 and waveguide 12 may be made as a single unit, but the preferred embodiment is to aflix the top and bottom portions of the tube to waveguide 12 and completely evacuate the air from both components. The waveguide may be of any size or shape and can be of the L, S, or X band type, with both ends of the waveguide being pro- 3 ,307,194 Patented Feb. 28, 1967 vided with a sealed window, with slot 14 preferably being one wavelength long, but may 'be of any length, depending on the specific design requirements and uses.

Tube 10 is essentially a typical, standard electron gun having a cathode 18, control grid 20, anode 22, focusing electrode 24, a second anode 26, deflection plates 28 and a collecting anode 30. Cathode 18 is connected to the collecting anode 30 through a current source such as a battery or the like, While deflection plates 28 have a voltage source impressed thereon in order to deflect the electron beam. By establishing a circuit between cathode 18 and anode 30, a difference of potential exists and a beam of electrons will be projected from the cathode to the anode and thus through slot 14 and across waveguide 12. If the intensity is made large enough, microwave energy projected into the waveguide will be reflected at the point where the electron beam crosses the slot, and will thereby be reflected back along the waveguide to an external R.-F. output. By impressing a deflection voltage on deflection plates 28, the electron beam is shifted in slot 14 either forwardly or rearwardly of the midpoint of the slot, there-by effecting a phase shift of the reflected energy, to an external R. -F. output. At all times it is necessary that the electron 'beam be parallel to the electric field vector. In order to accomplish a phase shift the electron beam density must be such that it behaves as a metallic conductor, i.e., a short circuit. In order to compute the density, etc., the following equations are set forth and the construction of the device is dependent upon the choice of parameters used and'the amount of microwave energy which is required to be projected to the outside R.-F. output.

(1) Electron beam density:

2 l' ozg D where: I a is the permittivity of free space 1 m is the electron mass Y e is the charge of an electron I n is the number of electrons per unit volum 2 mp: lne

where:

w is the plasma frequency which is the frequency at which the electrons oscillate about their rest positions (2) Power requirement:

' P ZAe zfi M d2e/m P available=KV FIG. 2 shows a typical block diagram arrangement, comprising a signal generator 32 which transmits a signal to a hybrid junction or directional coupler 34, to the electronic phase shifter 10, the instant invention, to a termination point 38 which may be an antenna, direct short, or a standard waveguide load. The signal is transmitted via an R.-F. transmission line 36 such as a waveguide, coaxial cable, or the like. If phase shifter is not emitting an electron beam across the waveguide 12, the R.-F. energy transmitted continues through the phase shifter to the termination point 38. However, if the phase shifter is emitting an electron beam across the path of the R.-F. energy, the energy will be reflected back to the junction point 34 and then to an R.-F. output 40 which may be an antenna, feedboard matrix, or the like. Since the phase angle is directly proportional to the length of path the R.-F. energy must travel, all that is required to shift the phase angle of the microwave energy to R.-F. output 40 is that the electron beam be deflected by means of deflection plates 28, thereby varying the length of path and thus effecting a phase change at the output. It is apparent, therefore, that if the junction 34 were not present, and microwave energy were required at termination point 38, hase shifter 10 could be used as an on-off switch simply by having the phase shifter emit, or not emit, electrons across the path of the R.-F. energy generated by the signal generator 32.

Referring now to FIG. 3, a system in block diagram arrangement is shown which has two phase shifters 10 in the path of the microwave energy generated by a signal generator 32 through a T network 42 to antennas 44 and 46. By varying the position of the electron beam in phase shifter 10, the phase in antennas 44 and 46 would likewise be shifted so as to provide a scanning arrangement. As can be seen, any number of the above combinations may be connected together to provide a very desirable scanning antenna. The scan rate would be governed only by the time required to deflect the almost inertialess electron beam emitted by phase shifter 10.

In summary, the invention encompasses an electron gun across a waveguide, with the electron gun being controlled by an external source separate from that of the microwave energy. Since the phase of the microwave energy (R.-F.) output is proportional to the position of the shorting beam, the desired energy (R.-F.) phase variation amplitude variation, or both, are accomplished by electrically moving the electron shorting beam, emitted by the electron gun, along a longitudinal slot in the waveguide. The time required to move the shorting beam is in the order of millimicroseconds (10' secs). Because the speed of moving the shorting beam is in millimicroseconds, the slow response time of the prior devices is overcome, and further, there is no limitation in the scan angle, or the number of targets which can be tracked, when used in a scanning antenna.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A phase shifting device comprising:

electron beam producing means,

transmission means having said electron beam producing means mounted upon a portion thereof,

said transmission means having a plurality of elongated slots oriented so as to allow said beam producing means to project a beam of electrons through said slots and across said transmission means, microwave signal means providing a signal into said transmission means, and

means to vary the path length of energy traveling within said transmission means including electron beam deflection means operative to move said electron beam along the length of said slots in a direction parallel to the path of said energy so that said energy impinges upon said beam of electrons at varied points along said transmission means thereby shifting the phase of said energy while maintaining the frequency of said energy at a constant value.

2. The device as described in claim 1 wherein said electron beam deflection means includes deflection plates having a deflection voltage impressed thereon.

3. A microwave system including at least one phase shifting device comprising:

electron beam producing means,

transmission means having said electron beam producing means mounted upon a portion thereof to provide a beam unit,

said transmission means having elongated slots, one each in the top and bottom, so as to allow said beam producing means to propel a beam of electrons through said slots and across said transmission means,

microwave signal means providing a signal into said beam unit,

means to vary the path length of said signal, said means including electron beam deflections means 0perative to move said electron beam along the length of said slots in a direction parallel to the path of said signal so that said signal impinges upon said beam of electrons at varied points along said transmission means thereby shifting the phase of said signal While maintaining the frequency of said signal at a constant value,

sealing means on each end of said portion of transmission means thereby permitting said unit to be evacuated, and

termination means, distinct from said microwave signal means, coupled to said transmission means whereby upon the signal intersecting said beam of electrons, said signal is reflected to said termination means.

4. The system of claim 3 wherein the electron beam producing means is mounted across said slots and wherein the longitudinal axis of said electron beam producing means is parallel to the electric field vector created by said microwave signal transmitted into said beam unit.

5. The system of claim 3 further including:

a plurality of said phase shifting devices,

a plurality of scanning antennas each coupled to a separate one of said phase shifting devices to provide phase differences to radiation emanating from said scanning antennas by introducing said beam of electrons into each of said phase shifting devices at different positions relative to their respective slots at the same instant of time.

References Cited by the Examiner UNITED STATES PATENTS 2,493,706 1/1950 Washburne et al 33258 2,576,696 11/1951 Ramo 332-25 2,897,459 7/1959 Stark 343-854 X ELI LIEBERMAN, Primary Examiner.

R. D. COHN, Assistant Examiner. 

1. A PHASE SHIFTING DEVICE COMPRISING: ELECTRON BEAM PRODUCING MEANS, TRANSMISSION MEANS HAVING SAID ELECTRON BEAM PRODUCING MEANS MOUNTED UPON A PORTION THEREOF, SAID TRANSMISSION MEANS HAVING A PLURALITY OF ELONGATED SLOTS ORIENTED SO AS TO ALLOW SAID BEAM PRODUCING MEANS TO PROJECT A BEAM OF ELECTRONS THROUGH SAID SLOTS AND ACROSS SAID TRANSMISSION MEANS, MICROWAVE SIGNAL MEANS PROVIDING A SIGNAL INTO SAID TRANSMISSION MEANS, AND MEANS TO VARY THE PATH LENGTH OF ENERGY TRAVELING WITHIN SAID TRANSMISSION MEANS INCLUDING ELECTRON BEAM DEFLECTION MEANS OPERATIVE TO MOVE SAID ELECTRON BEAM ALONG THE LENGTH OF SAID SLOTS IN A DIRECTION PARALLEL TO THE PATH OF SAID ENERGY SO THAT SAID ENERGY IMPINGES UPON SAID BEAM OF ELECTRONS AT VARIED POINTS ALONG SAID TRANSMISSION MEANS THEREBY SHIFTING THE PHASE OF SAID ENERGY WHILE MAINTAINING THE FREQUENCY OF SAID ENERGY AT A CONSTANT VALUE.
 3. A MICROWAVE SYSTEM INCLUDING AT LEAST ONE PHASE SHIFTING DEVICE COMPRISING: ELECTRON BEAM PRODUCING MEANS, TRANSMISSION MEANS HAVING SAID ELECTRON BEAM PRODUCING MEANS MOUNTED UPON A PORTION THEREOF TO PROVIDE A BEAM UNIT,
 5. THE SYSTEM OF CLAIM 3 FURTHER INCLUDING: A PLURALITY OF SAID PHASE SHIFTING DEVICES, A PLURALITY OF SCANNING ANTENNAS EACH COUPLED TO A SEPARATE ONE OF SAID PHASE SHIFTING DEVICES TO PROVIDE PHASE DIFFERENCES TO RADIATION EMANATING FROM SAID SCANNING ANTENNAS BY INTRODUCING SAID BEAM OF ELECTRONS INTO EACH OF SAID PHASE SHIFTING DEVICES AT DIFFERENT POSITIONS RELATIVE TO THEIR RESPECTIVE SLOTS AT THE SAME INSTANT OF TIME. 